This thesis has three chapters on international trade. The first chapter examines how trade policy can be contagious along a country’s supply chain. The chapter builds a theoretical model with vertical linkages to guide the empirical and quantitative analyses. Using trade protection and input-output tables from the US, the chapter finds that protection of inputs causes their output industries to demand protection as well, and that welfare losses generated by this type of cascading protection are substantial. The second chapter analyzes firms in international trade using Turkish firm-level data, and finds that import experience from a certain country can help a firm export to that country in the future. This chapter contributes to the literature by finding for the first time that firms can learn about potential clients through their existing suppliers. Finally, the third chapter focuses on the link between firms' exports versus domestic sales, and again using Turkish firm-level data, finds that exports and domestic sales are complementary even when they are composed of different products. This result indicates that firms that are credit constrained might be using their exports to internally finance their domestic operations.